It'll be round in a minute (6,4)
I believe the answer is:
second hand
'it'll be round in a minute' is the definition.
(as in a second hand on a clock)
'round in a minute' is the wordplay.
I cannot really see how this works, but
'round' could be 'hand' (I have seen 'Round of applause ' mean 'hand' so perhaps 'round' could also mean 'hand') and 'hand' is present in the answer.
'minute' could be 'second' (synonyms) and 'second' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for second hand that I've seen before include "not original" , "Not new - part of watch!" , "Pre-owned - used" , "being employed again" , "Pointer on dial" .)